【摘要】：固定式管板換熱器在壓力容器、石油、化工、暖通等各行業(yè)中得到了廣泛應(yīng)用。眾多換熱管和管板之間的焊縫導(dǎo)致?lián)Q熱器產(chǎn)生較大的焊接變形,如果控制不當(dāng),會(huì)惡化管板的受力狀態(tài),導(dǎo)致密封不嚴(yán),甚至管子拉脫等嚴(yán)重后果。因此預(yù)測(cè)和控制換熱器的焊接變形具有重要的工程應(yīng)用價(jià)值。本文設(shè)計(jì)組裝了旋轉(zhuǎn)焊接裝置,在此基礎(chǔ)上搭建了基于國(guó)產(chǎn)機(jī)器人的管板換熱器自動(dòng)化焊接試驗(yàn)平臺(tái),實(shí)現(xiàn)了單換熱管與管板的自動(dòng)焊接,獲得了良好焊縫成形的接頭;采用熱電偶測(cè)溫儀測(cè)量了焊趾附近指定點(diǎn)的溫度,獲得了這些點(diǎn)的熱循環(huán)曲線;利用盲孔法測(cè)量了焊縫附近應(yīng)力。采用Sysweld軟件建立了單換熱管與管板焊接的局部模型,對(duì)熱源進(jìn)行了校核。局部模型的計(jì)算結(jié)果表明,單換熱管焊接時(shí),殘余應(yīng)力呈中心對(duì)稱分布;在焊縫附近切向殘余應(yīng)力為拉應(yīng)力,隨著距焊縫距離增加逐步過(guò)渡為壓應(yīng)力;在焊縫附近徑向應(yīng)力為拉應(yīng)力,隨著距離焊縫越遠(yuǎn)徑向殘余應(yīng)力逐漸減小,在邊緣處徑應(yīng)力趨近于0。殘余塑性應(yīng)變主要分布在焊縫及熱影響區(qū)內(nèi),確定了以熱影響區(qū)邊界為準(zhǔn),確定宏單元尺寸。為了提高計(jì)算效率,根據(jù)換熱器的實(shí)際情況,提出縮小局部模型尺寸的方法。利用總散熱能量相等的原理計(jì)算并修正得到了等效散熱系數(shù),最終確定等效散熱系數(shù)為440W/(m2 · K)。利用逐步縮小范圍的方法確定了實(shí)際的彈性拘束大小,通過(guò)對(duì)不同影響因素的綜合分析,確定了軸向溫度力、拉壓剛度和彎曲剛度三個(gè)主要影響因素,以此為基礎(chǔ)擬合出了不同條件下的彈性拘束計(jì)算公式,并對(duì)公式進(jìn)行了驗(yàn)證。利用"局部-整體"映射有限元法對(duì)管板換熱器整體變形進(jìn)行預(yù)測(cè),研究了不同焊接順序?qū)附幼冃蔚挠绊?通過(guò)對(duì)5種焊接順序下的整體變形對(duì)比,得出:由內(nèi)向外對(duì)稱分布的焊接順序下,管板換熱器整體變形量最小。通過(guò)對(duì)比不同局部模型下管板換熱器的整體變形,驗(yàn)證了本文提出的縮小局部模型尺寸的方法的可行性。
[Abstract]:Fixed tubesheet heat exchanger has been widely used in pressure vessel, petroleum, chemical industry, HVAC and other industries. The welding seam between many heat exchanger pipes and tubesheet leads to large welding deformation of heat exchanger. If it is not controlled properly, it will deteriorate the stress state of tubesheet, resulting in lax sealing and even tube pulling off and so on. Therefore, it is of great engineering application value to predict and control the welding deformation of heat exchanger. In this paper, the rotating welding device is designed and assembled, on the basis of which the automatic welding test platform of tubesheet heat exchanger based on domestic robot is built, the automatic welding of single heat exchanger and tubesheet is realized, and the good weld forming joint is obtained. The temperature of the specified point near the welding toe was measured by thermocouple thermometer, and the thermal cycle curves of these points were obtained, and the stress near the weld was measured by blind hole method. The local model of welding between single heat exchanger pipe and tubesheet is established by Sysweld software, and the heat source is checked. The calculation results of the local model show that the residual stress is centrally symmetrical in the welding of the single heat exchanger pipe, and the tangential residual stress near the weld is tensile stress, which gradually changes to compressive stress with the increase of the distance from the weld. The radial stress near the weld is tensile stress, and the radial residual stress decreases gradually as the distance weld gets farther away, and the radial stress approaches to 0 at the edge of the weld. The residual plastic strain is mainly distributed in the weld and the heat affected zone, and the macro element size is determined based on the boundary of the heat affected zone. In order to improve the calculation efficiency, according to the actual situation of the heat exchanger, a method to reduce the size of the local model is put forward. Based on the principle of equal total heat dissipation energy, the equivalent heat dissipation coefficient is calculated and modified, and the equivalent heat dissipation coefficient is determined to be 440W/ (m2 K). The actual elastic restraint size is determined by the method of gradually narrowing the range. through the comprehensive analysis of different influencing factors, three main influencing factors, axial temperature force, tension and compression stiffness and bending stiffness, are determined. On this basis, the formulas for calculating elastic restraint under different conditions are fitted, and the formulas are verified. The "local-global" mapping finite element method is used to predict the overall deformation of tubesheet heat exchanger, and the influence of different welding sequence on welding deformation is studied. The global deformation under five welding sequences is compared. It is concluded that the overall deformation of tubesheet heat exchanger is the smallest under the welding sequence distributed symmetrically from inside to outside. By comparing the overall deformation of tubesheet heat exchanger under different local models, the feasibility of the method proposed in this paper to reduce the size of local model is verified.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG404

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本文編號(hào)：2480910